Carcass reinforcement for tire intended to bear heavy loads

ABSTRACT

A carcass reinforcement for a tire which is intended to bear heavy loads, comprising a composite fabric which comprises a rubber composition of reduced hysteresis and metal cables reinforcing the composition. The elastomeric matrix thereof comprises natural rubber or a synthetic polyisoprene in a majority proportion, and a reinforcing filler comprising a carbon black which meets all of the following conditions: 
     (i) 45≦CTAB specific surface area in m 2 /g (in accordance with Standard ASTM D3765-80)≦70,    (ii) 45≦BET specific surface area in m 2 /g (in accordance with Standard ASTM D4820-93)≦70, (iii) 45≦iodine adsorption index IA in mg/g (in accordance with Standard ASTM D1510-81)≦70, (iv) ratio (BET surface area/index IA)≦1.07, (v) 115≦DBP structure value in ml/100 g (in accordance with Standard ASTM D2414-93)≦170, (vi) 85 nm≦Stokes diameter dst in nm≦145, where dst is the diameter of aggregates corresponding to the maximum frequency of the Stokes diameters in a distribution of aggregates, and (vii) D50/dst≧0.0090. CTAB+0.19, where D50 is the difference, in the distribution of aggregates, between the Stokes diameters of two aggregates corresponding to one and the same frequency equal to 50% of the maximum frequency of the Stokes diameters, dst and D50 being measured by centrifugal photosedimentometry.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of PCT Application No.PCT/EP2003/010521, filed Sep. 22, 2003, published in French on Apr. 15,2004, as WO 2004/030946, which claims priority of French Application No.02/12213, filed Oct. 2, 2002, the entire contents of both applicationsbeing incorporated herein in their entirety.

FIELD OF THE INVENTION

The present invention relates to a carcass reinforcement for a tirewhich is intended to bear heavy loads, such as a heavy-vehicle orconstruction-machinery tire, and to such a heavy-vehicle orconstruction-machinery tire.

DESCRIPTION OF RELATED ART

Radial-carcass tires for motor vehicles bearing heavy loads, inparticular for heavy vehicles, comprise reinforcements which are formedof reinforcing threads or plies of metal wires coated with elastomers.More precisely, these tires comprise, in their bottom zone, one or morebead wires, a carcass reinforcement extending from one bead wire to theother and, in their crown, a crown reinforcement comprising at least twocrown plies.

These heavy-vehicle tires are designed to be able to be retreaded one ormore times when the treads which they comprise reach a critical degreeof wear after prolonged travel, which involves having a carcassreinforcement which has not been subject to significant damage, for eachtire to be retreaded the tread of which has reached this degree of wear.

When running under heavy load, the “band” of the carcass (central zoneon either side of the median circumferential plane of the tire) issubjected to flexural stresses which may be very high, hence thenecessity of imparting a high mechanical strength to this “band”, andthe bottom zone of the tire (close to each of the two upturns of thecarcass) may be the seat of operating temperatures which are also veryhigh, hence the necessity of imparting reduced hysteresis to this bottomzone.

Consequently, with the aim of minimising the embrittlement of the tireand of delaying the appearance of damage therein, a carcassreinforcement of heavy-vehicle type must be both as cohesive aspossible, to resist the mechanical stresses during travel, and of as lowhysteresis as possible, to minimise the heating during travel and alsoto limit the thermochemical and possibly thermo-oxidising change of theinternal compositions.

It is known to the person skilled in the art that the use, in a rubbercomposition for a heavy-vehicle carcass reinforcement and in a quantityof approximately 50 phr (parts by weight per hundred parts ofelastomer(s)), of a relatively structured grade 300 carbon black, suchas the black N347, or a less structured one, such as the black N326,makes it possible to improve the cohesion, endurance and hysteresis ofthis composition, which imparts a longer life to the carcassreinforcement and, consequently, to the corresponding heavy-vehicletire.

It is also known that coarse carbon blacks, such as the black N539, onlyimpart sufficient cohesion to a heavy-vehicle carcass reinforcementcomposition if these blacks are present in this composition in a verylarge quantity, which may have the undesirable effect of adverselyaffecting the hysteresis of this composition.

Japanese patent specification JP-A-04/274 901 discloses the use ofspecific carbon blacks in rubber compositions which are equally wellintended for at least three distinct zones of a tire having specificallya reduced weight, for imparting to this lightweight tire improvedproperties of rolling resistance and reinforcement, compared with thoseexhibited by a tire the same zones of which comprise compositions eachcomprising a grade 300 carbon black.

These specific carbon blacks have a specific surface area N₂SA (measuredin accordance with Standard ASTM D3037 of 1984) of from 60 to 84 m²/g, a“DBP” structure value (measured in accordance with Standard JIS K 6221)of from 120 to 200 m/100 g and they have a surface chemistry which issuch that the ratio “N₂SA/IA” of said specific surface area to theiodine adsorption index “IA” (also measured in accordance with StandardJIS K 6221) is equal to or greater than 1.10.

Japanese patent specification JP-A-02/103 268 discloses the use ofcarbon blacks to improve the hysteresis and reinforcement properties ofrubber compositions for carcass reinforcements for any tires, or evenmore generally intended for damping vibrations.

These carbon blacks have a CTAB specific surface area (measured inaccordance with Standard ASTM D3765-80) of from 50 to 75 m²/g, a “DBP”structure value (measured in accordance with Standard JIS K 6221) equalto or greater than 105 ml/100 g and they have a surface chemistry whichis such that the ratio “N₂SA/IA” of the specific surface area “N₂SA”(measured in accordance with Standard ASTM D3037-86) to the iodineadsorption index “IA” (measured in accordance with Standard JIS K 6221)is equal to or greater than 1.10.

It will be noted that these last two documents do not relate to tiresintended to bear heavy loads, and certainly not to a carcassreinforcement of the type having metal cables which is specificallyintended to be fitted on such heavy-vehicle or construction-machinerytires.

SUMMARY OF THE INVENTION

The object of the present invention is to propose a novel carcassreinforcement for a tire which is intended to bear heavy loads, such asa heavy-vehicle or construction-machinery tire, this reinforcementcomprising a composite fabric which comprises a cross-linkable orcross-linked rubber composition having a reduced hysteresis in thecross-linked state and metal cables reinforcing this composition.

This object is achieved in that the Applicants have recentlysurprisingly discovered that the association, with an elastomeric matrixcomprising natural rubber or a synthetic polyisoprene in a majorityproportion, of a reinforcing filler comprising a carbon black whichmeets all the following conditions:

-   (i) 45≦CTAB specific surface area in m²/g (in accordance with    Standard ASTM D3765-80)≦70,-   (ii) 45≦BET specific surface area in m²/g (in accordance with    Standard ASTM D4820-93)≦70,-   (iii) 45≦iodine adsorption index IA in mg/g (in accordance with    Standard ASTM D1510-81)≦70-   (iv) ratio (BET surface area/index IA)≦1.07,-   (v) 115≦DBP structure value in ml/100 g (in accordance with Standard    ASTM D2414-93)≦170,-   (vi) 85 nm≦Stokes diameter dst in nm≦145,    where dst is the diameter of aggregates corresponding to the maximum    frequency of the Stokes diameters in a distribution of aggregates,    and-   (vii) D50/dst≧0.0090. CTAB+0.19,

where D50 is the difference, in the distribution of aggregates, betweenthe Stokes diameters of two aggregates corresponding to one and the samefrequency equal to 50% of the maximum frequency of the Stokes diameters,dst and D50 being measured by centrifugal photosedimentometry,

makes it possible to obtain a rubber composition which has in thecross-linked state improved hysteresis properties at high deformations,in comparison with the hysteresis properties of known compositionscomprising a grade 300 carbon black and having substantially one and thesame modulus of elongation at low deformation.

It will be noted that the carcass reinforcement according to theinvention comprises a carbon black having a ratio (BET surfacearea/index IA) of reduced value and a ratio D50/dst which increases withthe CTAB specific surface area, these ratios imparting respectively tothe blacks according to the invention a surface chemistry and amorphology which are particularly suitable.

DETAILED DESCRIPTION OF THE INVENTION

The elastomeric matrix of the rubber composition according to theinvention may advantageously be formed of natural rubber or syntheticpolyisoprene, or alternatively of a blend of natural rubber or syntheticpolyisoprene with one or more other diene elastomers.

In this second case, the natural rubber or the synthetic polyisoprene ispresent in a majority proportion in the matrix, that is to say in aquantity greater than 50 phr (parts by weight per hundred parts ofelastomers). Preferably, the natural rubber or the polyisoprene ispresent in a quantity equal to or greater than 70 phr.

Among the diene elastomers which may be used in a blend with the naturalrubber or the synthetic polyisoprene, mention may be made of the dieneelastomers, whether functional or not, belonging to the group consistingof polybutadienes, copolymers of styrene and butadiene (SBR) prepared insolution or in emulsion, copolymers of butadiene and isoprene (BIR) andterpolymers of styrene, butadiene and isoprene (SBIR).

Preferably, the polybutadiene used comprises a majority of cis-1,4linkages and the SBR used comprises a majority of trans-1,4 linkages.

These elastomers may be modified during polymerisation or afterpolymerisation by means of branching agents such as divinylbenzene, orcoupling or starring agents such as carbonates, halo-tins,halo-silicons, or alternatively by means of functionalising agentsresulting in grafting on the chain or at the chain end of hydroxyl,carbonyl, carboxyl groups or alternatively of amine groups (for exampleby means of dimethylamino-benzophenone or diethylamino-benzophenone asfunctionalising agent).

According to another characteristic of the invention, said carbon blackfurthermore satisfies the following condition:

-   (viii) 80≦DBPC structure value in ml/100 g (in accordance with    Standard ASTM D3493-91)≦130,    DBPC being measured after 4 compressions at 24,000 psi.

Preferably, said carbon black furthermore meets the following condition:

-   (ix) 85≦DBPC structure value in ml/100 g≦125.

Preferably, the carbon black used in the composition according to theinvention furthermore meets the following three conditions:

-   (x) 50≦CTAB specific surface area in m²/g≦65,-   (xi) 50≦BET specific surface area in m²/g≦65,-   (xii) 50≦iodine adsorption index IA in mg/g≦65.

Equally preferably, said carbon black furthermore meets the condition:

-   (xiii) ratio (BET surface area)/(index IA)≦1.05.

Equally preferably, said carbon black furthermore meets the condition:

-   (xiv) 120≦DBP structure value in ml/100 g≦165.

Equally preferably, said carbon black furthermore meets the condition:

-   (xv) 90 nm≦Stokes diameter dst in nm≦140.

Equally preferably, said carbon black furthermore meets the condition:

-   (xvi) D50/dst≧0.0092. CTAB+0.21.

The values dst and D50 are measured by means of a centrifugalphotosedimentometer of type “DCP” (Disk Centrifuge Photosedimentometer),sold by Brookhaven Instruments. The operating method for thesemeasurements is as follows:

A sample of carbon black is dried, in accordance with Standard JIS K6221(1975). Then 10 mg of carbon black thus dried is suspended in 40 ml ofan aqueous solution of 15% ethanol and 0.05% of a non-ionic surfactant(by volume).

The dispersion of carbon black is obtained by ultrasound treatment for10 minutes, by means of a 600 Watt ultrasonic probe. To this end anultrasound generator designated “Vibracell ½ inch” sold by Bioblock andadjusted to 60% of its power (namely to 60% of maximum amplitude) isused.

A gradient solution composed of 15 ml water (with 0.05% non-ionicsurfactant) and 1 ml ethanol is injected into the disc of thesedimentometer, rotating at 8,000 rpm, then 0.30 ml of the suspension ofcarbon black is injected on to the surface of the gradient solution. Themass size distribution curve is recorded for 120 minutes. A softwareprogram provides said values dst and D50 in nm.

The carbon black according to the invention may be used on its own asreinforcing filler, or alternatively in a blend with a reinforcingorganic filler and/or a reinforcing inorganic filler. The quantity ofcarbon black used may vary from 30 phr to 70 phr and, preferably, from35 to 65 phr.

In the case of a blend with a reinforcing organic or inorganic filler,said carbon black is present in a majority proportion in the reinforcingfiller (i.e. in a mass fraction greater than 50%). Preferably, the massfraction of carbon black in the reinforcing filler is greater than 70%.

According to a particularly advantageous embodiment of the invention,the reinforcing organic filler comprises a methylene acceptor/donorsystem (what is called an “M.A.D.” system), which designates compoundssuitable for reacting together to generate a three-dimensionalreinforcing resin by condensation.

In known manner, the term “methylene acceptor” designates the reactantwith which the methylene donor compound reacts by formation of methylenebridges (—CH2—), upon the curing of the composition, thus resulting inthe formation in situ of the three-dimensional resin lattice. Themethylene acceptor must be capable of dispersing perfectly in theelastomeric matrix.

Particularly suitable as methylene acceptors are phenols, the genericname for hydroxylated derivatives of arenes, and the equivalentcompounds. This definition covers in particular monophenols, for examplephenol or hydroxybenzene, bisphenols, polyphenols (polyhydroxyarenes),substituted phenols such as alkylphenols or aralkylphenols, for examplebisphenols, diphenylolpropane, diphenylolmethane, naphthols, cresol,t-butylphenol, octylphenol, nonylphenol, xylenol, resorcinol oranalogous products.

Preferably phenolic resins referred to as “novolac resins”, also calledphenol-aldehyde precondensates, resulting from the precondensation ofphenolic compounds and aldehydes, in particular formaldehyde, are usedas methylene acceptor. In known manner, these novolac resins (alsoreferred to as “two-step resins”) are thermoplastic and require the useof a curing agent (methylene donor) to be cross-linked, unlike, forexample, Resols® which are thermohardening; they have sufficientplasticity not to interfere with the processing of the rubbercomposition. After cross-linking by the methylene donor (they may thenbe referred to as “thermohardened” novolac resins), they arecharacterised in particular by a tighter three-dimensional lattice thanthat of the Resols®.

The quantity of methylene acceptor must be between 1 and 10 phr; below 1phr, the technical effect desired is inadequate, whereas beyond 10 phrthere are risks of excessive stiffening and excessive compromising ofthe hysteresis. For all these reasons, a quantity of between 1.5 and 8phr is more preferably selected, amounts lying within a range from 2 to4 phr being particularly advantageous.

A curing agent, capable of cross-linking or hardening the methyleneacceptor previously described, also commonly referred to as “methylenedonor”, must be associated with this acceptor.

Preferably, the methylene donor is selected from the group consisting ofhexamethylenetetramine (“HMT”), hexamethoxymethylmelamine (“H3M”),hexaethoxymethylmelamine, formaldehyde polymers such as p-formaldehyde,N-methylol derivatives of melamine, or mixtures of these compounds. Morepreferably, this donor is selected from among HMT, H3M or a mixture ofthese compounds.

The quantity of methylene donor must be between 0.5 and 5 phr; below 0.5phr, the technical effect desired is inadequate, whereas beyond 5 phrthere are risks of compromising the processing in the uncured state ofthe compositions (for example, problem of solubility of the HMT) or ofthe vulcanisation (slowing in the presence of H3M). For these reasons, aquantity of between 0.5 and 3.5 phr is more preferably selected, amountslying within a range from 1 to 3 phr being particularly advantageous.

Finally, the quantity of methylene donor, in the aforementioned ranges,is advantageously adjusted so as to represent between 10% and 80%, morepreferably within a range from 40 to 60%, by weight relative to thequantity of methylene acceptor.

In the present application, “reinforcing inorganic filler”, in knownmanner, is understood to mean an inorganic or mineral filler, whateverits colour and its origin (natural or synthetic), also referred to as“white” filler or sometimes “clear” filler in contrast to carbon black,this inorganic filler being capable, on its own, without any other meansthan an intermediate coupling agent, of reinforcing a rubber compositionintended for the manufacture of tires, i.e. capable of replacing aconventional tire-grade carbon black filler in its reinforcementfunction.

Preferably, all or at the very least a majority proportion of thereinforcing inorganic filler is silica (SiO₂). The silica used may beany reinforcing silica known to the person skilled in the art, inparticular any precipitated silica having a BET surface area and a CTABspecific surface area both of which are less than 450 m²/g, even if thehighly dispersible precipitated silicas are preferred. Even morepreferably, the silica has BET or CTAB specific surface areas both ofwhich are from 70 to 250 m²/g and, preferably, from 80 to 240 m²/g.

The BET specific surface area of the silica is determined in knownmanner, in accordance with the method of Brunauer, Emmett and Tellerdescribed in “The Journal of the American Chemical Society” vol. 60,page 309, February 1938, corresponding to Standard AFNOR-NFT 45007(November 1987); the CTAB specific surface area is the external surfacearea determined in accordance with the same Standard AFNOR-NFT-45007 ofNovember 1987.

“Highly dispersible silica” is understood to mean any silica having avery substantial ability to disagglomerate and to disperse in anelastomeric matrix, which can be observed in known manner by electron oroptical microscopy on thin sections. As non-limitative examples of suchpreferred highly dispersible silicas, mention may be made of the silicas[sic] Perkasil KS 430 from Akzo, the silicas BV3380 and BV3370GR fromDegussa, the silicas Zeosil 1165 MP and 1115 MP from Rhodia, the silicaHi-Sil 2000 from PPG, the silicas Zeopol 8741 or 8745 from Huber, andtreated precipitated silicas such as, for example, the aluminium-“doped”silicas described in European patent specification EP-A-0 735 088.

Other silicas which are not highly dispersible, such as the silicaPerkasil KS404 from Akzo and the silicas Ultrasil VN2 or VN3, may alsobe used.

The physical state in which the reinforcing inorganic filler is presentis immaterial, whether it be in the form of a powder, microbeads,granules or alternatively balls. Of course, “reinforcing inorganicfiller” is also understood to mean mixtures of different reinforcinginorganic fillers, in particular of highly dispersible silicas such asdescribed above.

As reinforcing inorganic filler, it is also possible to use, althoughthis is not limiting, aluminas (of formula Al₂O₃), such as the aluminasof high dispersibility which are described in European patentspecification EP-A-810 258, or alternatively aluminium hydroxides, suchas those described in international patent specification WO-A-99/28376.

Also suitable as reinforcing inorganic fillers are carbon blacksmodified by silica, such as, although this is not limiting, the fillerssold by CABOT under the name “CRX 2000”, which are described ininternational patent specification WO-A-96/37547.

In the event that the carbon black according to the invention is used ina blend with a reinforcing inorganic filler, the rubber compositionaccording to the invention may furthermore comprise in conventionalmanner a reinforcing inorganic filler/elastomeric matrix bonding agent(also referred to as coupling agent), the function of which is to ensuresufficient chemical and/or physical bonding between said inorganicfiller and the matrix, while facilitating the dispersion of theinorganic filler within the matrix.

“Coupling agent” is more precisely understood to mean an agent capableof establishing a sufficient chemical and/or physical connection betweenthe filler in question and the elastomer, while facilitating thedispersion of this filler within the elastomeric matrix. Such a couplingagent, which is at least bifunctional, has, for example, the simplifiedgeneral formula “Y-T-X”, in which:

-   -   Y represents a functional group (“Y” function) which is capable        of bonding physically and/or chemically with the inorganic        filler, such a bond being able to be established, for example,        between a silicon atom of the coupling agent and the surface        hydroxyl (OH) groups of the inorganic filler (for example,        surface silanols in the case of silica);    -   X represents a functional group (“X” function) which is capable        of bonding physically and/or chemically with the elastomer, for        example by means of a sulphur atom;    -   T represents a group making it possible to link Y and X.

Silica/elastomer coupling agents in particular have been described in alarge number of documents, the best known being bifunctionalalkoxysilanes such as polysulphurised alkoxysilanes.

As polysulphurised alkoxysilanes, mention will be made more particularlyof the polysulphides (in particular disulphides, trisulphides ortetrasulphides) of bis-((C₁-C₄)alkoxyl-(C₁-C₄)alkylsilyl-(C₁-C₄)alkyl),such as for example the polysulphides of bis(3-trimethoxysilylpropyl) orof bis(3-triethoxysilylpropyl). Of these compounds, in particularbis(3-triethoxysilylpropyl) tetrasulphide, abbreviated TESPT, of theformula [(C₂H₅O)₃Si(CH₂)₃S₂]₂, or bis(triethoxysilylpropyl) disulphide,abbreviated TESPD, of the formula [(C₂H₅O)₃Si(CH₂)₃S]₂, are used. TESPDis sold, for example, by Degussa under the names Si266 or Si75 (in thelatter case, in the form of a mixture of disulphide (75% by weight) andof polysulphides), or alternatively by Witco under the name SilquestA1589. TESPT is sold, for example, by Degussa under the name Si69 (orX50S when it is supported to 50% by weight on carbon black), oralternatively by Osi Specialties under the name Silquest A1289 (in bothcases, a commercial mixture of polysulphides having an average value ofn close to 4). Mention will also be made of tetrasulphurisedmonoalkoxysilanes, such as monoethoxydimethylsilylpropyl tetrasulphide(abbreviated to MESPT), which are the subject of international patentapplication PCT/EP02/03774.

The compositions according to the invention are capable of cross-linkingunder the action of sulphur, peroxides or bismaleimides with or withoutsulphur. They may also contain the other constituents conventionallyused in rubber mixes, such as a conventional non-reinforcing inorganicfiller (for example clay, bentonite, talc, chalk, kaolin or titaniumoxides), plasticisers, pigments, antioxidants, processing agents,cross-linking accelerators such as benzothiazole derivatives,diphenylguanidine and, in the present case of rubber compositions forcarcass reinforcements provided to have satisfactory adhesion to metal,a cobalt salt and/or a silica/resin association.

The compositions according to the invention may be prepared using knownthermomechanical working processes for the constituents in one or morestages. For example, they may be obtained by thermomechanical working inan internal mixer in one stage which lasts from 3 to 7 minutes, with aspeed of the blades of 50 rpm, or in two stages which last from 3 to 5minutes and from 2 to 4 minutes respectively, this thermomechanicalworking being followed by mechanical working or a finishing stageeffected at about 80° C., during which the sulphur, the vulcanisationaccelerators (in the case of a sulphur-cross-linked composition) andpossibly said cobalt salt are incorporated.

In the event that a reinforcing organic filler of type methyleneacceptor/donor system is used in the composition according to theinvention, the methylene donor is only introduced during the step ofmechanical working, unlike the methylene acceptor, which is introducedduring the thermomechanical working.

The carcass reinforcement according to the invention is preferably suchthat, in the composite fabric used as heavy-vehicle orconstruction-machinery carcass ply, the density of the metal cables isof between 15 and 100 cables per dm of radial ply and the distancebetween two adjacent radial cables, from axis to axis, is preferably ofbetween 1 and 6 mm.

In a heavy-vehicle carcass ply, this cable density is preferably ofbetween 40 and 100 cables per dm, more preferably between 50 and 80cables per dm, and the distance between two adjacent radial cables, fromaxis to axis, is preferably of between 1.0 and 2.5 mm, more preferablybetween 1.25 and 2 mm.

In a construction-machinery carcass ply, this cable density ispreferably of between 15 and 70 cables per dm, more preferably between20 and 35 cables per dm, and the distance between two adjacent radialcables, from axis to axis, is preferably of between 2 and 6 mm, morepreferably between 2.5 and 5.5 mm.

These cables according to the invention are preferably arranged suchthat the width (“1”) of the rubber bridge between two adjacent cables isof between 0.25 mm and 1.5 mm. In a heavy-vehicle carcass ply, the width1 is more preferably of between 0.25 and 1 mm and, in aconstruction-machinery carcass ply, this width 1 is more preferably ofbetween 0.25 and 1.5 mm.

This width 1 in known manner represents the difference between thecalendering pitch (laying pitch of the cable in the rubber fabric) andthe diameter of the cable. Below the minimum value indicated, the rubberbridge, which is too narrow, risks mechanically degrading during workingof the ply, in particular during the deformation which it experiences inits own plane by extension or shearing. Beyond the maximum indicated,there are risks of flaws in appearance occurring on the sidewalls of thetires or of penetration of objects, by perforation, between the cables.

For these reasons, the width 1 is even more preferably selected to bebetween 0.35 and 0.85 mm, be it for a heavy-vehicle orconstruction-machinery carcass ply.

Equally preferably, the rubber composition of this composite fabric has,in the cross-linked state (i.e., after curing) and measured inaccordance with Standard ASTM D 412, a secant tensile modulus M10 whichis less than 12 MPa, more preferably of between 5 and 11 MPa. It iswithin such a field of moduli that the best compromise of endurance inthe composite fabrics of the carcass reinforcement has been recorded.

A heavy-vehicle or construction-vehicle tire according to the inventionis such that it comprises this carcass reinforcement.

This heavy-vehicle or construction-machinery tire comprises in knownmanner a crown, two sidewalls and two beads, each of these beads beingreinforced by a bead wire. The crown is conventionally reinforced by acrown reinforcement formed for example of at least two superposedcrossed plies, reinforced by metal cables. The carcass reinforcement iswound around the two bead wires within each bead, the upturn of thereinforcement being for example arranged towards the outside of thetire.

The carcass reinforcement is formed of at least one ply reinforced byso-called “radial” metal cables, that is to say that they are arrangedpractically parallel to each other and extend from one bead to theother, forming an angle of between 80° and 90° with the mediancircumferential plane (plane perpendicular to the axis of rotation ofthe tire which is located halfway between the two beads and passesthrough the centre of the crown reinforcement).

The aforementioned characteristics of the present invention, as well asothers, will be better understood on reading the following descriptionof several examples of embodiment of the invention, which are given byway of illustration and not of limitation.

In these examples, the properties of the compositions are evaluated asfollows:

Mooney Viscosity

The Mooney viscosity ML (1+4) is measured in accordance with StandardASTM D1646 (1999).

Shore A Hardness

The Shore A hardness is measured in accordance with standard ASTM D2240(1997).

Moduli of Elongation

The moduli of elongation are measured at 10% (M10) at a temperature of23° C. in accordance with Standard ASTM D412 (1998) on ASTM C testpieces. These are true secant moduli in MPa, that is to say the secantmoduli calculated reduced to the real cross-section of the test piece atthe given elongation.

Break Indices

These indices are measured at 100° C. The properties at break, breakingstress FR in MPa and elongation at break AR in % are measured inaccordance with Standard ASTM D412 (1998). The measurements are carriedout on ASTM C test pieces.

Tearability Indices

These indices are measured at 100° C. The breaking load (FRD) in N/mm ofthickness and the elongation at break (ARD) in % are measured on a testpiece of dimensions 10×105×2.5 mm notched at its centre over a depth of5 mm.

Hysteresis Losses (HL)

They are measured in % by rebound at 60° C. at the sixth impact, inaccordance with the equation:HL (%)=100×(W ₀ −W ₁)/W ₁, with W ₀: energy supplied and W ₁: energyrestored.

Dynamic Properties

The dynamic characteristics of the materials are analysed on a Schenckmachine, in accordance with Standard ASTM D 5992 (1996). The response ofa sample of vulcanised material (cylindrical test piece of a thicknessof 4 mm and a section of 400 mm²), subjected to an alternating singlesinusoidal shearing stress, at a frequency of 10 Hz and at 60° C., isrecorded. Scanning is effected at an amplitude of deformation of 0.1 to50% (outward cycle), then of 50% to 0.1% (return cycle). The maximumshear modulus G*max in MPa and the maximum value of the tangent of theloss angle tan delta max is determined during the outward cycle.

EXAMPLES OF EMBODIMENT OF THE INVENTION 1) First Series of Examples

The object of these examples is to compare compositions based on naturalrubber (NR hereafter) reinforced with carbon black, with quantities ofblack of from 52 to 58 phr. These compositions are specified in Table 1hereafter (in phr).

The “control” composition 1 is representative of the known prior art,and comprises 52 phr of black N347 as reinforcing filler.

Compositions 2 to 7 according to the invention comprise a carbon black Afor compositions 2 to 5, or a carbon black B for compositions 6 and 7.

Carbon black A is sold under the name “CRX1416B” by CABOT, and carbonblack B is sold under the name “EX 3-3” by COLUMBIAN.

Composition 5 differs from composition 4 in that it furthermorecomprises a processing aid sold by RHEIN CHEMIE under the name “AFLUX42”, in order to reduce the viscosity of composition 5 in thenon-cross-linked state).

All these compositions are sulphur-cross-linkable. TABLE 1 Comp. 1 Comp.2 Comp. 3 Comp. 4 Comp. 5 Comp. 6 Comp. 7 NR 100 100 100 100 100 100 100Black N347 52 Black A 52 55 58 58 Black B 55 58 ZnO 9 9 9 9 9 9 9Stearic acid 0.65 0.65 0.65 0.65 0.65 0.65 0.65 Antioxidant 1.50 1.501.50 1.50 1.50 1.50 1.50 “AFLUX 42” 3 Cobalt salt* 0.20 0.20 0.20 0.200.20 0.20 0.20 Insoluble 7.6 7.6 7.6 7.6 7.6 7.6 7.6 sulphur Accelerator0.93 0.93 0.93 0.93 0.93 0.93 0.93*phr of cobalt metal

The natural rubber (NR) which is used is peptised and has a Mooneyviscosity ML (1+4) at 100° C. equal to 60.

The antioxidant used isN-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine.

The carbon blacks used are set forth in Table 2 below: TABLE 2 N347Black A Black B CTAB in m²/g 88 55 50 BET in m²/g 88 53 50 IA in mg/g 9062 56 BET/IA 0.98 0.85 0.89 DBP in ml/100 g 124 134 130 DBPC in ml/100 g100 94 88 dst in nm 77 131 133 D50 in nm 53 103 113 D50/dst 0.688 0.7860.849

These compositions 1 to 7 are obtained by mixing all the aforementionedconstituents, except for the cobalt salt, the sulphur and theaccelerator, by thermomechanical working in an internal mixer in onestep which lasts approximately 4 minutes with a speed of rotation of theblades of 50 rpm, until a dropping temperature of approximately 170° C.is reached, followed by a finishing step effected at 80° C., duringwhich the cobalt salt, the sulphur and the vulcanisation accelerator areincorporated.

The cross-linking is effected at 150° C. for a time sufficient toachieve 99% of the maximum torque on a rheometer.

The properties in the cross-linked state and in the non-cross-linkedstate of these compositions 1 to 7 were compared. The results are setforth in Table 3 below. TABLE 3 Comp. 1 Comp. 2 Comp. 3 Comp. 4 Comp. 5Comp. 6 Comp. 7 ML(1 + 4) at 100° C. 52 52 55 58 52 48 52 Shore 80 78 8081 81 77 79 M10 in MPa 9.13 7.67 8.03 8.94 9.49 8.27 8.92 as base 100100 84 88 98 104 89 96 HL in % 22.85 17.13 17.13 18.05 18.96 16.85 18.00as base 100 100 75 75 79 83 74 79 G* max 60° C. 8.24 5.76 6.43 8.82 8.04as base 100 100 70 78 107 97 Tan delta max 60° C. 0.163 0.130 0.1320.142 0.139 as base 100 100 80 81 87 85 Break 100° C. FR in MPa 16.014.7 14.1 15.1 14.1 14 14 AR in % 360 360 326 323 308 359 364Tearability 100° C. FRD in N/mm 30 33 38 34 25 36 29 ARD in % 97 84 8787 77 88 85

It would appear that the carbon blacks A or B impart to compositions 4,5 and 7 according to the invention hysteresis properties at highdeformation (HL at 60° C.) which are improved by 17% to 21% relative tothose of the “control” composition comprising the black N347, thesecompositions according to the invention furthermore having a modulus ofelongation at low deformation (M10) which is close to that of said“control” composition, which makes these compositions according to theinvention particularly well suited for use in the carcass reinforcementof tires intended to bear heavy loads.

It will be noted that the other properties of these compositions 4, 5and 7 according to the invention are comparable to those of said“control” composition.

It will also be noted that the incorporation in the composition 5 of theprocessing aid imparts to this composition 5 a viscosity in thenon-cross-linked state and, consequently, a processing ability which issimilar to that of the “control” composition, and practically withoutadversely affecting the hysteresis properties of this composition 5.

2) Second Series of Examples

The object of the following examples is to compare two rubbercompositions each having in the cross-linked state a secant tensilemodulus M10 of approximately 6 MPa, which are both based on naturalrubber and which comprise respectively two different carbon blacks asreinforcing filler, in a quantity of black of between 40 and 50 phr.

The first composition 8 is a “control” composition representing theknown prior art, and it comprises 45 phr of carbon black designated“N326”.

The second composition 9 is in accordance with the invention, and itcomprises 48 phr of said carbon black A designated “CRX1416B”.

Table 4 below lists the characteristics of these carbon blacks N326 andA. TABLE 4 N326 Black A CTAB in m²/g 83 55 BET in m²/g 84 53 IA in mg/g82 62 BET/IA 1.02 0.85 DBP in ml/100 g 72 134 DBPC in ml/100 g 69 94 dstin nm 72 131 D50 in nm 54 103 D50/dst 0.75 0.786

It will be noted that this black N326 is such that D50/Dst does not meetthe aforementioned condition (vii) according to the invention, since0.75 is less than 0.0090. CTAB+0.19=0.937.

The formulations of these compositions 8 and 9 are set forth in Table 5below. TABLE 5 Comp. 8 Comp. 9 NR 100 100 Black N326 45 Black A 48 ZnO7.50 7.50 Stearic acid 0.90 0.90 Antioxidant 1.50 1.50 Cobalt salt* 0.200.20 Insoluble sulphur 5.60 5.60 Accelerator 0.93 0.93*phr of cobalt metal

The natural rubber (NR) which is used is peptised and has a Mooneyviscosity ML (1+4) at 100° C. equal to 60.

The antioxidant used isN-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine.

These compositions 8 and 9 are obtained by mixing all the aforementionedconstituents, except for the cobalt salt, the sulphur and theaccelerator, by thermomechanical working in an internal mixer in onestage, of a duration of about 4 minutes with a speed of rotation of theblades of 50 rpm, until a dropping temperature of approximately 170° C.is obtained, followed by a finishing step effected at 80° C., duringwhich are incorporated the cobalt salt, the sulphur and thevulcanisation accelerator.

The cross-linking is effected at 150° C. for a time sufficient toachieve 99% of the maximum torque on a rheometer.

The properties in the cross-linked state and in the non-cross-linkedstate of these compositions 8 and 9 were compared. The results are setforth in Table 6 below. TABLE 6 Composition 8 Composition 9 ML(1 + 4) at100° C. 89 85.5 M10 in MPa 5.8 6.3 as base 100 100 109 HL in % 18.5 14.2as base 100 100 77 Break at 100° C.: FR in MPa 17.5 15.0 AR in % 530 425Tearability at 100° C.: FRD in N/mm 29.0 36.5 ARD in % 130 180

It would appear that the carbon black A imparts to the composition 9according to the invention hysteresis properties at high deformation (HLat 60° C.) which are improved by 23% (going from 18.5% to 14.2%)compared with those of the “control” composition 8 comprising the blackN326, this composition 9 furthermore having a modulus of elongation atlow deformation (M10) which is close to that of said composition 8,which makes said composition 9 particularly well suited for use in thecarcass reinforcement of tires intended to bear heavy loads.

It will be noted that the other properties of this composition 9according to the invention are comparable to those of said “control”composition 8.

3) Third Series of Examples

The object of the following examples is also to compare two rubbercompositions each having in the cross-linked state a secant tensilemodulus M10 of approximately 6 MPa, which are both based on naturalrubber and which comprise respectively two different carbon blacks asreinforcing filler, in a quantity of black of between 40 and 50 phr.

The first composition 10 is a “control” composition representing theknown prior art, and it comprises 47 phr of carbon black designated“N326”.

The second composition 11 is in accordance with the invention, and itcomprises, on one hand, 47 phr of said carbon black A of the name“CRX1416B” and, on the other hand, 1 phr of a methylene donor and 2 phrof a methylene acceptor as reinforcing organic filler.

The formulations of these compositions 10 and 11 are set forth in Table7 below. TABLE 7 Composition 10 Composition 11 NR 100 100 Black N326 47Black A 47 ZnO 7.5 9 Stearic acid 0.9 0.5 Antioxidant 1.5 1.8 Cobaltsalt* 0.2 0.15 “Methylene acceptor” 2 “Methylene donor” 1 Insolublesulphur 5.6 3.13 Accelerator 0.93 0.6*phr of cobalt metal

The natural rubber (NR) which is used is peptised and has a Mooneyviscosity ML (1+4) at 100° C. equal to 60.

The antioxidant used isN-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine.

The methylene acceptor is a “novolac” phenolic resin sold by INSPECunder the name “Penacolite B20”.

The methylene donor is hexamethylenetetramine.

These compositions 10 and 11 are obtained by mixing all theaforementioned constituents, except for the cobalt salt, the sulphur,the accelerator and the methylene donor, by thermomechanical working inan internal mixer in one stage, of a duration of about 4 minutes with aspeed of rotation of the blades of 50 rpm, until a dropping temperatureof approximately 170° C. is obtained, followed by a finishing stepeffected at 80° C., during which are incorporated the cobalt salt, thesulphur, the vulcanisation accelerator and the methylene donor.

The cross-linking is effected at 140° C. for a time sufficient toachieve 99% of the maximum torque on a rheometer.

The properties in the cross-linked state and in the non-cross-linkedstate of these compositions 10 and 11 were compared. The results are setforth in Table 8 below. TABLE 8 Composition 10 Composition 11 ML(1 + 4)at 100° C. 78 94 M10 in MPa 5.9 5.8 as base 100 100 98 HL in % 18.1 14.6as base 100 100 81 Break at 100° C.: FR in MPa 16.7 15.8 AR in % 490 500Tearability at 100° C.: FRD in N/mm 24.9 35.1 ARD in % 155 153

It would appear that the carbon black A imparts to the composition 11according to the invention hysteresis properties at high deformation (HLat 60° C.) which are improved by 19% (going from 18.1% to 14.6%)compared with those of the “control” composition 10 comprising the blackN326, this composition 11 furthermore having a modulus of elongation atlow deformation (M10) which is close to that of the composition 10,without impairing the cohesion properties (break and tearability), whichmakes this composition 11 according to the invention particularly wellsuited for use in the carcass reinforcement of tires intended to bearheavy loads.

1. A carcass reinforcement for a tire which is intended to bear heavyloads, said reinforcement comprising a composite fabric which comprisesa cross-linkable or cross-linked rubber composition having a reducedhysteresis in the cross-linked state and metal cables reinforcing saidcomposition, which comprises: an elastomeric matrix comprising naturalrubber or a synthetic polyisoprene in a majority proportion, and areinforcing filler comprising a carbon black, wherein said carbon blackmeets all of the following conditions: (i) 45≦CTAB specific surface areain m²/g (in accordance with Standard ASTM D3765-80)≦70, (ii) 45≦BETspecific surface area in m²/g (in accordance with Standard ASTMD4820-93)≦70, (iii) 45≦iodine adsorption index IA in mg/g (in accordancewith Standard ASTM D1510-81)≦70 (iv) ratio (BET surface area/indexIA)≦1.07, (v) 115≦DBP structure value in ml/100 g (in accordance withStandard ASTM D2414-93)≦170, (vi) 85 nm≦Stokes diameter dst in nm≦145,where dst is the diameter of aggregates corresponding to the maximumfrequency of the Stokes diameters in a distribution of aggregates, and(vii) D50/dst≧0.0090. CTAB+0.19, where D50 is the difference, in thedistribution of aggregates, between the Stokes diameters of twoaggregates corresponding to one and the same frequency equal to 50% ofthe maximum frequency of the Stokes diameters, dst and D50 beingmeasured by centrifugal photosedimentometry.
 2. The carcassreinforcement according to claim 1, wherein said carbon blackfurthermore meets the following condition: (viii) 80≦DBPC structurevalue in ml/100 g (in accordance with Standard ASTM D3493-91)≦130, thevalue DBPC being measured after 4 compressions at 24,000 psi.
 3. Thecarcass reinforcement according to claim 2, wherein said carbon blackfurthermore meets the following condition: (ix) 85≦DBPC structure valuein ml/100 g≦125.
 4. The carcass reinforcement according to claim 1,wherein said carbon black further meets the following conditions: (x)50≦CTAB specific surface area in m²/g≦65, (xi) 50≦BET specific surfacearea in m²/g≦65, (xii) 50≦iodine adsorption index IA in mg/g≦65.
 5. Thecarcass reinforcement according to claim 1, wherein said carbon blackfurther meets the following condition: (xiii) ratio (BET surfacearea)/(index IA)≦1.05.
 6. The carcass reinforcement according to claim1, wherein said carbon black further meets the following condition:(xiv) 120≦DBP structure value in ml/100 g≦165.
 7. The carcassreinforcement according to claim 1, wherein said carbon black furthermeets the following condition: (xv) 90 mn≦Stokes diameter dst in nm≦140.8. The carcass reinforcement according to claim 1, wherein said carbonblack further meets the following condition: (xvi) D50/dst≧0.0092. CTAB+0.21.
 9. The carcass reinforcement according to claim 1, wherein theelastomeric matrix comprises natural rubber or synthetic polyisoprene.10. The carcass reinforcement according to claim 1, wherein saidelastomeric matrix comprises a blend of natural rubber or of syntheticpolyisoprene with at least one diene elastomer, optionally functional,belonging to the group consisting of polybutadienes, copolymers ofstyrene and butadiene prepared in solution or in emulsion, copolymers ofbutadiene and isoprene and terpolymers of styrene, butadiene andisoprene, the natural rubber or the synthetic polyisoprene being presentin said composition in a quantity equal to or greater than 70 phr(phr:parts by weight per hundred parts of elastomers).
 11. The carcassreinforcement according to claim 1, wherein said carbon black is presentin said reinforcing filler in a mass fraction greater than 50% and lessthan or equal to 100%.
 12. The carcass reinforcement according to claim11, wherein said carbon black is present in said reinforcing filler in amass fraction of from 70% to 100%.
 13. The carcass reinforcementaccording to claim 11, wherein said reinforcing filler comprises a blendof said carbon black and a reinforcing inorganic filler.
 14. The carcassreinforcement according to claim 13, wherein said reinforcing inorganicfiller is a silica.
 15. The carcass reinforcement according to claim 13,wherein said reinforcing filler which comprises a blend of said carbonblack and a reinforcing organic filler further comprises a methylenedonor/methylene acceptor system.
 16. The carcass reinforcement accordingto claim 15, wherein said composition comprises: between 30 phr and 70phr of said carbon black, between 1 phr and 10 phr of said methyleneacceptor, and between 0.5 phr and 5 phr of said methylene donor.
 17. Thecarcass reinforcement according to claim 15, wherein said methyleneacceptor is a phenolic resin.
 18. The carcass reinforcement according toclaim 17, wherein said phenolic resin is a novolak phenolic resin. 19.The carcass reinforcement according to claim 15, wherein said methylenedonor is selected from the group consisting of hexamethylenetetramine,hexamethoxymethylmelamine, hexaethoxymethylmelamine, para-formaldehydepolymers, N-methylol melamine derivatives, and mixtures of thesecompounds.
 20. A carcass reinforcement according to claim 1, whereinsaid composite fabric comprises said metal cables in a cable density ofbetween 15 and 100 cables per dm of fabric.
 21. The carcassreinforcement according to claim 20, wherein the distance between twoadjacent radial cables, from axis to axis, is of between 1 and 6 mm. 22.The carcass reinforcement according to claim 21, wherein the width 1 ofa rubber bridge between two adjacent cables is between 0.25 and 1.5 mm.23. The carcass reinforcement according to claim 22, wherein said width1 of the rubber bridge is between 0.35 and 0.85 mm.
 24. The carcassreinforcement according to claim 1, wherein said rubber composition has,in the cross-linked state and measured in accordance with Standard ASTMD 412, a secant tensile modulus M10 which is less than 12 MPa.
 25. Thecarcass reinforcement according to claim 24, wherein said rubbercomposition has, in the cross-linked state and measured in accordancewith Standard ASTM D 412, a secant tensile modulus M10 which is ofbetween 5 and 11 MPa.
 26. The carcass reinforcement according to claim20, wherein said cable density is between 50 and 80 cables per dm offabric, said reinforcement being intended for a heavy-vehicle tire. 27.The carcass reinforcement according to claim 26, wherein the distancebetween two adjacent radial cables, from axis to axis, is between 1.25and 2 mm.
 28. The carcass reinforcement according to claim 20, whereinsaid cable density is of between 20 and 35 cables per dm of fabric, saidreinforcement being intended for a construction-machinery tire.
 29. Thecarcass reinforcement according to claim 28, wherein the distancebetween two adjacent radial cables, from axis to axis, is between 2.5and 5.5 mm.
 30. A tire for a vehicle intended to bear heavy loads whichcomprises a carcass reinforcement according to claim
 1. 31. A tire for aheavy vehicle, which comprises a carcass reinforcement according toclaim
 26. 32. A tire for construction machinery, which comprises acarcass reinforcement according to claim 28.